Adware can degrade computer performance and track user's habits

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NEW YORK — Marketers appeared to be directly responsible for more than half of the pop-up and other online advertisements run through so-called adware networks, reducing the companies' ability to plausibly deny knowledge of that connection, a report has found.

Critics say adware has become one of the top scourges of Internet use because it can degrade computer performance, track a user's browsing habits and mysteriously appear on computers without a user's full knowledge. Major companies often blame an intermediary when they are found to advertise through such programs.

But the Center for Democracy and Technology, a nonprofit group that has conducted research on such programs, said Wednesday that 55 percent of the ads, particularly those coming from smaller companies, used no intermediaries at all.

"There are a lot of companies that are clearly working directly with adware companies," said Ari Schwartz, deputy director for the center.

The report did not name the advertisers.

Researchers studied the patterns by loading two computers with adware and installing a packet logger to track the Web addresses accessed.

When there is an intermediary, the software would visit one site, which would pull information from another site, which would possibly retrieve the actual ad from a third location. When adware gets the ad from the first site, there likely isn't an intermediary.

Schwartz acknowledged, however, that the finding is possibly inflated because the study does not take into account intermediaries that pass along ads via e-mail. In such cases, the ad would appear to come directly from the company, even when an intermediary was used.